Aircraft gas turbine engines include various components requiring lubrication. A main lubrication system normally provides lubricant to these components. It is desirable to also provide an emergency lubrication capability so that at least some components can be lubricated, at least temporarily, if the main lubrication system fails or operates abnormally. Irrespective of whether the main lubrication system is operating normally or not, it may also be desirable to ensure that components are not starved of lubricant during reduced-G conditions. Reduced-G conditions are those in which G, the acceleration due to gravity (9.8 meters/sec./sec.), is partially or entirely counteracted by aircraft maneuvers and/or aircraft orientation.